1. Field of the Invention
This invention relates to a control device case for use with a control device of a comparatively small size such as an invertor device.
2. Description of the Prior Art
Control devices such as invertor devices for controlling a motor of a comparatively small capacity frequently employ a case of the type wherein a heat generating element such as a semiconductor module element is secured directly to a case body on which cooling fins are formed so that the case may also serve as a cooler for cooling the heat generating element of the control device.
One of such control device case is disclosed, for example, in Japanese Utility Model Laid-Open No. 176565/1980 and is shown in FIGS. 9 and 10. Referring to FIGS. 9 and 10, the control device case includes a case body 1 having a base wall 1c. A plurality of cooling fins 1a in the form of vertical ribs are formed on a rear face of the base wall 1c of the case body 1 while a pair of cooling fins 1b in the form of vertical ribs are formed on a front face of the base wall 1c. The cooling fins 1b serve also as the opposite side walls of the body 1. A pair of shoulders or steps 1d are formed on the front side of the base wall 1c, and a prepared hole groove 1e is formed in each step 1d. Such a prepared hole groove 1e is formed also along a front end of each of the cooling fins 1b. A printed circuit board 2 is placed on the steps 1d of the base wall 1c of the case body 1 and is secured to the latter by means of a plurality of self-tapping screws 6 screwed into the prepared hole grooves 1e on the steps 1d. Several electric or electronic parts are mounted on the printed circuit board 2. For example, a pair of terminal blocks 3 are mounted at upper and lower portions of a front face of the printed circuit board 2 while a pair of semiconductor module elements 4 such as power transistors which generate heat when energized are mounted on a rear face of the printed circuit board 2. The control device case further includes a cover 5 secured to the case body 1 by means of another plurality of self-tapping screws 6 screwed into the prepared hole grooves 1e at the front ends of the cooling fins 1b. The printed circuit board 2 is thus confined in a spacing defined by the case body 1 and the cover 5.
The case body 1 is produced by cutting an extrusion molded material or bar of aluminum which has such a cut end as shown as a section of the case body 1 in FIG. 10. The prepared hole grooves 1e on the steps 1d and cooling fins 1b are formed upon such extrusion molding of aluminum.
When the control device is to be actually used, that is, if connecting lines (not shown) to a power source and a motor (not shown) which is to be controlled by the control device are connected to the terminal blocks 3 in order to control the motor, the semiconductor module elements 4 and some other heat generating members are energized to generate heat. The heat thus generated is transmitted to the case body 1 and then radiated from the cooling fins 1a and 1b of the case body 1 to the external air. Thus, the larger the capacity of the motor, the more heat which is generated by the heat generating members, and accordingly, the larger the total heat radiating area of the cooling fins 1a and 1b must be made. This factor necessairly increases the size of the case body 1.
Also, with the structure shown in FIGS. 9 and 10, the cover 5 must be removed before the connecting lines (not shown) to the terminal blocks 3 are connected. Also, it is difficult to form mounting legs by way of which the case body 1 is to be secured to a wall (not shown) of a room or the like.
Also, since the case body 1 is made of aluminum, which is high in heat conductivity, an operator inadvertently touching with the case body 1 may be burnt by the case body 1 due to heat generated by the heat generating members.
Since the conventional control device case is constructed in such a manner as described above, it is disadvantageous in that the size of the control device case must be made comparatively large with respect to heat generation by the semiconductor elements built therein as the capacity of an object which is to be controlled increases. Also, operation of a member such as a terminal block mounted on the printed circuit board and formation of an opening through which wires to the terminal block are threaded are difficult. Further, where the case body of the control device case is made of a metal, it is a drawback that an operator may inadvertently touch and be burned by the case body which is in a comparatively high temperature condition due to generation of heat from the semiconductor elements.